1. Field of the Invention
The present invention is related to a self-adjusting vapor outlet system and method that assists in determining a material shut-off level in a container, such as a vehicle fuel tank.
2. Background Art
When refueling gas in a tank, most systems have an automatic shut-off feature. Basically, near a tip of a nozzle there is a small hole and a small pipe leads back from the hole into a handle of the nozzle. Suction is applied to this pipe using a venturi. When the tank is not full, air is being drawn through the hole by a vacuum, and the air flows easily. When gasoline in the tank rises high enough to block the hole, a mechanical linkage in the handle senses the change in suction and shuts-off the nozzle.
FIG. 1 shows a conventional fuel tank system 100. Filling of a fuel tank 102 is achieved by inserting a pressure-sensitive nozzle (not shown) that is in fluid communication with a fuel filler pipe 104 and a supply of fuel (not shown). Upon insertion of the pressure-sensitive nozzle into a neck of fuel filler pipe 104, fuel 106 is delivered from filler pipe 104 in the direction of arrow A until fuel flow is stopped by an operator or based on fuel 106 in the container reaching a predetermined (e.g., automatic shut-off based on a pressure sensitive nozzle) level 108. During this process, the space 110 in fuel tank 102 above a surface 112 of fuel 106 becomes occupied by fuel vapor. Vapor must be displaced via the fuel tank vent 114 for fuel 106 to enter the fuel tank 102. When vent opening 116 of vent 114 is closed, fuel 106 will fill up filler pipe 104 until reaching the pressure sensitive nozzle (not shown). Once the pressure sensitive nozzle is reached, auto shut-off if instigated.
A fuel shut-off level 108 is reached when the rising surface 112 of fuel 106 in fuel tank 102 is higher than an open end 116 of vent tube 114. Before reaching fuel shut-off level 108, the amount of vapor pressure approximates ambient atmospheric pressure because of unobstructed relief through vent tube 114. Beyond fuel shut-off level 108, if more fuel 106 were delivered into fuel tank 102 from the supply through the pressure-sensitive filler pipe nozzle, the vapor pressure in space 110 above fuel 106 in fuel tank 102 would rise because the fuel vapor has no means of escape through vent tube 114. In response to the build-up of fuel vapor pressure, fuel flows in the direction of arrow C, the pressure-sensitive nozzle terminates the delivery of fuel 106 into fuel tank 102.
As seen in FIG. 2, if system 100 is positioned at an incline with respect to a ground surface 200 over a predetermined angle (e.g., a 2° incline is a tolerance established for refueling of automobiles, while sport utility vehicles can have greater incline angles), there can be a substantially reduced chance breather tube 114 will be properly positioned with respect to surface 112. Again, proper positioning is when surface 112 blocks open end 116 of breather tube 114 at the predetermined cutoff level 108. Thus, when breather tube 114 and surface 112 are not properly positioned due to the incline, vapor removal will continue through breather tube 114, until fuel 106 has passed predetermined cutoff level 108. Hence, the vapor escape path is hydraulically closed. The fuel level will increase slightly as it continues up breather tube 114. When this occurs, an auto-shutoff mechanism in the pressure-sensitive nozzle, which is usually triggered by detecting a differential in filling pressure through the filling gun inserted in input tube 104, will actuate. This can cause an early shut-off and/or inadequate filing of fuel tank 102.
Therefore, what is needed is a system associated with a vent tube of a fuel tank that accurately responds to fuel level regardless of an incline of the fuel tank with respect to a ground plane.